Feed injector

ABSTRACT

This invention relates to an apparatus and process for atomizing a petroleum feed. More particularly, a liquid petroleum feed is atomized with an atomization apparatus in which the apparatus has an orifice that produces a generally flat spray pattern of finely dispersed feed prior to contacting catalyst in a fluid catalytic cracking zone. The orifice has a general aspect ratio greater than 1.0 and a ratio of perimeter length-to-cross-sectional area greater than 1.5 relative to a perimeter-to-cross-sectional area ratio of a circular orifice of equivalent area. The apparatus can be used to atomize feed injected into the cracking zone of a fluid catalytic cracker.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 60/590,599 filed Jul. 23, 2004.

FIELD OF THE INVENTION

This invention relates to an apparatus for atomizing a petroleum feed.More particularly, a liquid petroleum feed is atomized with anatomization apparatus in which the apparatus has an orifice thatproduces a generally flat spray pattern of finely dispersed feed priorto contacting catalyst in a fluid catalytic cracking zone.

BACKGROUND OF THE INVENTION

The fluidization of petroleum feeds is important to petroleum processessuch as fluidized catalytic cracking (FCC) and coking. In the FCCprocess, high molecular weight feeds are contacted with fluidizedcatalyst particles in the riser reactor part of the FCC unit. Thecontacting between feed and catalyst is controlled according to the typeof product desired. In the catalytic cracking of the feed, reactorconditions such as temperature and contact time are controlled tomaximize the products desired and minimize the formation of lessdesirable products such as light gases and coke.

Since the contacting between catalyst and feed in the FCC reactor istypically in the order of a few seconds, an important factor governingthe efficiency of the cracking process is the catalyst. Catalyst for theFCC process is well known and may be either amorphous or crystalline.Catalyst entering the FCC reactor is typically fluidized using steam,hydrocarbon gases generated during the cracking process or somecombination thereof. The reaction of catalyst and feed generates largevolumes of gaseous hydrocarbons and spent catalyst bearing cokedeposits. The gas/solid mixture is passed to separators, typicallycyclones, where spent catalyst is separated from gases. Gases are thenprocessed to recover desired hydrocarbons and spent catalyst sent forregeneration.

Because of the short contacting time between feed and catalyst, thecondition of the feed is also important. The type of feed injection canhave an impact on the product slate produced by the FCC reactor. Thereare two pathways for the feed to crack into gaseous hydrocarbons, i.e.,catalytic and thermal. Thermal cracking in a FCC unit is generallyundesirable as this type cracking can result in the generation of lightgases such as methane in addition to coke. In order to improve theefficiency of the catalytic cracking process, it is generally desirableto have the feed dispersed into fine droplets as a non-dispersed liquidfeed in contact with hot catalyst particles favors thermal cracking.

One method of achieving droplets of feed involves the use of steam toform a dispersion of droplets. The resulting dispersion is a two-phasesystem of water and hydrocarbon that is sprayed through nozzle(s) intothe FCC riser reactor where it contacts fluidized hot catalyst. Theprocess of forcing a fluid under pressure through the orifice of anozzle to form a fine dispersion of fluid droplets is known asatomization. The degree of atomization is a function of nozzle design,orifice size, fluid density, fluid viscosity, surface tension andpressure drop across the orifice. Generally, using a nozzle with asmaller orifice favors decreasing droplet size. Increasing the degree ofatomization for heavy (viscous) petroleum fractions which form at leasta part of the feed to the FCC process is especially challenging.

There have been numerous designs of nozzles for feed atomization in theFCC reactor. Some proposed nozzle designs utilize swirl vanes, either inthe nozzle itself or the conduit leading to the nozzle. Another proposeddesign uses a Venturi in the conduit feeding the nozzle. Other proposeddesigns include feeding hydrocarbon and feed concentrically through thenozzle, a hydrocarbon feed distributor feeding hydrocarbon throughconcentric nozzles located in the center of the FCC reactor, injectingfeed through a plurality of orifices within the nozzle and the use ofshrouds around the nozzles, and controlling the angle at which the steamand hydrocarbon contact one another. It has also been proposed to form atwo-phase fluid mixture of feed and steam, dividing the fluid into twoseparate streams which are passed through an impingement mixing zone, ashear mixing zone to recombine the separate streams and a low pressureatomization zone. A further proposed design is a nozzle in which mistingof a single feed stream may be accomplished by passing the full liquidstream, with or without included steam, through deflection vanes tocreate a free vortex in a single full-flow centrifugal or helicalacceleration chamber which terminates in a sharp or square-edgedorifice. Such orifice is substantially smaller in diameter than thefluid supply line for feeding the liquid hydrocarbons directly into thecatalyst flow stream in the riser reactor. Finally, a feed injector thatis generally fan-shaped has been proposed for producing a substantiallyflat spray pattern of atomized feed.

There is still a need for improved performance of feed injection nozzlesto create improvements in the atomization process of feeds in the FCCprocess.

SUMMARY OF THE INVENTION

This invention is directed to an apparatus for atomizing and dispersinga petroleum feed to a FCC reactor. In one embodiment, the inventionrelates to an apparatus for atomizing a petroleum feed comprising: aconduit containing at least one inlet, at least one outlet and apassageway within said conduit connecting the inlet with the outlet,said passageway containing an orifice wherein the orifice has a generalaspect ratio greater than 1.0 and a ratio of perimeterlength-to-cross-sectional area greater than 1.5 relative to aperimeter-to-cross-sectional area ratio of a circular orifice ofequivalent area. The spray pattern produced by the feed passing throughthe orifice is substantially flat and fan-shaped.

In a related embodiment of the invention, the orifice is elliptical orrectangular in shape and the elliptical or rectangular shape includes atleast one member protruding inwardly from the elliptical or rectangularshape. In a preferred embodiment, the inwardly protruding membercomprises at least one pointed, square-edged or rounded member.

In another embodiment, the invention comprises a process for injecting apetroleum feed into a reaction zone of a fluid catalytic crackingreactor which comprises: injecting the feed into the reaction zonethrough a feed injector for atomizing the feed, said injector comprisinga conduit containing at least one inlet, at least one outlet and atleast one orifice, said orifice having a general aspect ratio greaterthan 1.0 and having a ratio of perimeter length-to-cross-sectional areagreater than 1.5 relative to the perimeter-to-cross-sectional area ratioof a circular orifice of equivalent area. The feed injector results in aspray pattern of atomized particles that is generally flat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a top view of the injector in planview.

FIG. 2 is a schematic diagram of a side view of the injector in planview.

FIG. 3 is a schematic diagram of a front view of the injector in planview.

FIG. 4 is a schematic diagram of the injector in profile.

FIG. 5 is a graph showing a comparison of relative droplet size as afunction of injector design.

DETAILED DESCRIPTION

A conventional FCC process includes a riser reactor and a regeneratorwherein petroleum feed is injected into the reaction zone of a riserreactor containing a bed of fluidized cracking catalyst particles. Thecatalyst particles typically contain zeolites and may be fresh catalystparticles, catalyst particles from a catalyst regenerator, or somecombination thereof. Gases that may be inert gases, hydrocarbon vapors,steam, or some combination thereof, are normally employed as lift gasesto assist in fluidizing the hot catalyst particles.

Catalyst particles that have contacted feed produce product vapors andcatalyst particles containing strippable hydrocarbons as well as coke.The catalysts exit the reaction zone as spent catalyst particles and areseparated from the reactor's effluent in a separation zone. Theseparation zone for separating spent catalyst particles from reactoreffluent may employ separation devices such as cyclones. Spent catalystparticles are stripped of strippable hydrocarbons using a strippingagent such as steam. The stripped catalyst particles are then sent to aregeneration zone in which any remaining hydrocarbons are stripped andcoke is removed. In the regeneration zone, coked catalyst particles arecontacted with an oxidizing medium, usually air, and coke is oxidized(burned) at high temperatures such as 510 to 760° C. The regeneratedcatalyst particles are then passed back to the riser reactor.

Suitable hydrocarbon feedstocks for the catalytic cracking processdescribed herein include natural and synthetic hydrocarbonaceous oilsboiling in the range of about 221° C. (430° F.) to about 566° C. (1050°F.), such as gas oil; heavy hydrocarbonaceous oils comprising materialsboiling above 1050° F.; heavy and reduced petroleum crude oil; petroleumatmospheric distillation bottoms; petroleum vacuum distillation bottoms;pitch, asphalt, bitumen, other heavy hydrocarbon residues; tar sandoils; shale oil; liquid products derived from coal liquefactionprocesses, naphtha, and mixtures thereof.

FCC catalysts may be amorphous, e.g., silica-alumina and/or crystalline,e.g., molecular sieves including zeolites or mixtures thereof Apreferred catalyst particle comprises (a) an amorphous, porous solidacid matrix, such as alumina, silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silica-beryllia, silica-titania,silica-alumina-rare earth and the like; and (b) a zeolite such asfaujasite. The matrix can comprise ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, magnesia andsilica-magnesia-zirconia. The matrix may also be in the form of a cogel.Silica-alumina is particularly preferred for the matrix, and can containabout 10 to 40 wt. % alumina. As discussed, promoters can be added.

The catalyst's zeolite includes zeolites which are iso-structural tozeolite Y. These include the ion-exchanged forms such as the rare-earthhydrogen and ultrastable (USY) form. The zeolite may range incrystallite size from about 0.1 to 10 microns, preferably from about 0.3to 3 microns. The relative concentrations of zeolite component andmatrix on an anhydrous basis may vary widely, with the zeolite contentranging from about 1 to 100, preferably 10 to 99, more usually fromabout 10 to 80, percent by weight of the dry composite.

The amount of zeolite component in the catalyst particle will generallyrange from about 1 to about 60 wt. %, preferably from about 5 to about60 wt. %, and more preferably from about 10 to about 50 wt. %, based onthe total weight of the catalyst. As discussed, the catalyst istypically in the form of a catalyst particle contained in a composite.When in the form of a particle, the catalyst particle size will rangefrom about 10 to 300 microns in diameter, with an average particlediameter of about 60 microns. The surface area of the matrix materialafter artificial deactivation in steam at pressures higher than incommercial operations (i.e., at pressures of ca. 1 atmosphere) will beabout ≦350 m²/g, preferably 50 to 200 m²/g, more preferably from about50 to 100 m²/g. While the surface area of the catalysts will bedependent on such things as type and amount of zeolite and matrixcomponents used, it will usually be less than about 500 m²/g, preferablyfrom about 50 to 300 m²/g, more preferably from about 50 to 250 m²/g,and most preferably from about 100 to 250 m²/g.

FCC process conditions in the reactor's reaction zone includetemperatures from about 450° C. to about 700° C., hydrocarbon partialpressures from about 10 to 40 psia (69 to 276 kPa), preferably fromabout 20 to 35 psia (138 to 241 kPa); and a catalyst to feed (wt/wt)ratio from about 3 to 100, where catalyst weight is total weight of thecatalyst composite. The total pressure is from atmospheric to about 45psig (411 kPa). Though not required, it is preferred that steam beconcurrently introduced with the feedstock into the reaction zone, withthe steam comprising up to about 50 wt. %, preferably about 2 to about10 wt. % of the primary feed. Also, it is preferred that the feedstock'sresidence time in the reaction zone be less than about 20 seconds,preferably from about 0.1 to about 20 seconds, and more preferably fromabout 1 to about 5 seconds.

In order for feed to be converted to product in such short reactionstimes, it is important for the feed to be atomized into small particles.The efficiency of the cracking process for converting feed to product isa function of the physical properties of the feed (viscosity, densityand the like), physical properties of the catalyst stream (nature andconfiguration of catalyst), feed particle size, particle distributioninto the reaction zone, spray angles between feed particles and catalystparticles, process conditions including flow rates of gases and liquidsand pressures, and injector design. Additional factors that influenceinjector design include liquid pressure drops across the injectororifice, relative velocity between feed and any gas added to aidatomization and ratio of gas to liquid. Thus the efficiency of thecracking process is dependent in part on the type and design of the feedinjector. The injector should atomize and disperse feed particles aswell as be durable, i.e., capable of extended periods of service withoutplugging or suffering undue mechanical wear, e.g., abrasion from contactwith catalyst particles. In the FCC process, feed is injected into thefluidized stream of catalyst particles through at least one injectorsituated to allow efficient contact between feed particles and catalystparticles. In a preferred embodiment, multiple feed injectors aresituated in a pattern surrounding the stream of fluidized catalystparticles.

The feed is normally pre-heated to temperatures of from 120 to 450° C. Agas or gases is preferably added to the feed to enhance the atomizationprocess. Such gases include steam, nitrogen, hydrogen, FCC off-gas andlower molecular weight (C₆—) hydrocarbons, preferably steam. The ratioof steam to feed can influence the atomization process by controllingthe density of the resulting feed/steam mixture. The amount of steam isgenerally in the range from about 0.1 to 5.0 wt. %, based on the weightof the feed/steam mixture.

The feed injector according to the invention includes a conduitcontaining at least one inlet, at least one outlet and at least oneorifice, said orifice having a general aspect ratio greater than 1.0 andhaving a ratio of perimeter length-to-cross-sectional area greater than1.5 relative to the perimeter-to-cross-sectional area ratio of acircular orifice of equivalent area. The inlet accepts feed and anyatomizing enhancing gas. The feed or feed mixture passes through theinlet to a throat section that is connected to an orifice. Upon passingthrough the orifice, an unstable jet of liquid is formed which breaks upinto droplets (is atomized) and exits the injector through an outlet.

The orifice contains a single opening having a general aspect ratio ofgreater than 1.0, preferably greater than 1.5, most preferably greaterthan 2.0. The general aspect ratio of the orifice is defined as thelargest linear measurement across the orifice opening orthogonal to theflow into which the injection is occurring divided by the largest linearmeasurement across the orifice opening perpendicular to the orthogonalmeasurement and within the planar surface of the orifice. For example, acircle or square would have a general aspect ratio of 1. The orificealso has a perimeter length-to-cross-section area ratio greater than1.5, preferably greater than 2.0, most preferably greater than 2.5relative to the perimeter-to-area ratio of a circular orifice ofequivalent area. The circular orifice of equivalent area is obtained bymeasuring the open flow area of the orifice, calculating the diameter ofa circle having the same open area, and dividing the circumference ofthe circle of the resulting diameter by the area of the circle ofresulting diameter. The resulting perimeter-to-area ratio constitutes abasis for comparison with orifices according to the invention.

The orifice shape according to the above-noted criteria does not includea circle or square. An orifice in the shape of a rectangle or ellipsecould meet the criteria provided that the perimeter of rectangle orellipse is irregular, i.e., is interrupted by at least one protrusionwhich can have a square edged, rectangular, pointed or rounded shape. Apreferred embodiment is a rectangle or ellipse having more than oneprotrusion. An example would be a rectangle-shaped orifice wherein atleast portion of at least one side of the orifice has a saw-toothedpattern in which the individual teeth can be pointed, rectangular,square or rounded. The same pattern could be applied to an ellipse.Other geometric shapes are within the scope of invention provided theymeet above-noted criteria.

An embodiment of the present feed injector is shown in FIG. 1 which is aschematic diagram in plan view. A feed 10 is carried through conduit 12to inlet 14 of feed injector 16. The feed may be a mixture of heatedhydrocarbon and admixed gas such as steam as atomizing aid. The conduit12 is typically a feed-carrying pipe which is welded or otherwiseattached to feed injector 16 at injector inlet 14. Injector 16 containsan orifice 18. Orifice 18 is bounded by a plurality of rectangularprojections 20. The profile of orifice 18 is shown as a convex curvewhose curvature is similar to that of fan-shaped outlet 22. Outlet 22 isin the plane of the drawing. Feed entering inlet 14 contacts projections20 where the feed is atomized and discharged as an atomized spraythrough fan-shaped outlet 22.

FIG. 2 is a further schematic in plan view of a side view of theinjector of FIG. 1. In the side view, the injector has been rotated 90°along an axis running through the center of the inlet and outlet. As inFIG. 1, a feed 10 is carried through conduit 12 to inlet 14 of feedinjector 16. The conduit 12 is typically a feed-carrying pipe which iswelded or otherwise attached to feed injector 16 at injector inlet 14.Injector 16 contains an orifice 18. Orifice 18 is the opening defined bythe plurality of rectangular projections 20. Feed entering inlet 14contacts projections 18 where the feed is atomized and dischargedthrough the opening 24 in outlet 22 as an atomized spray.

FIG. 3 is a schematic diagram of a front view of feed injector 16. Theoutlet is shown as the rectangle shape 22 having an inner wall 24 and anouter wall 26. The orifice is shown as bounded by the rectangle havingsides 28 and 30. Inside the boundaries of orifice 18 are a multiplicityof protrusions 20 having a rectangular shape and arranged along the twosides 28 in a saw-toothed pattern. The flow of feed is orthogonal(perpendicular) to the planar figure of the injector, i.e., the flowwould be coming at right angles from below the plane of the paper andexiting at right angles above the plane of the paper. According to thedefinition set forth hereinbefore, the general aspect ratio of theorifice is defined as the largest linear measurement across the orificeopening orthogonal to the flow into which the injection is occurringdivided by the largest linear measurement across the orifice openingperpendicular to the orthogonal measurement and within the planarsurface of the orifice. In the context of FIG. 3, the ratio of dottedline a to dotted line b (a:b) is greater than 1. If hypothetically theratio were 1, then orifice 18 would be in the form of a square insteadof the rectangle of FIG. 3. The perimeter length-to-cross-sectional areais determined by calculating the area bounded by the protrusions 20which corresponds to the open flow area of the orifice 18. The diameterof a circle having the same open area can be determined since the areaof a circle is equal to πr². The circumference of the circle is equal toπD. The perimeter-to-area ratio is then obtained by dividing thecircumference by the area.

FIG. 4 is a schematic view of the injector in profile. In FIG. 4,feed-carrying conduit 12 is attached to injector 16 at 14. Projections20 are within outlet 22 but are recessed below the surface of outlet 22.The depth relation between projections 20 and outlet 22 are also shownin FIG. 1.

The present feed injector or injectors are situated on the wall of theriser reactor. The feed injector or injectors are attached to the wallof the riser reactor such that the spray pattern of atomized feed fromthe injector(s) contact the fluidized catalyst particles flowing throughthe reaction zone of the riser reactor. The injector(s) are attached tothe conduit carrying feed to the riser reactor. It is preferred thatmultiple feed injectors be employed to increase efficiency of feeddistribution to flowing catalyst particles. Such multiple feed injectorsare normally employed in a ring around the riser reactor, preferably ina symmetric radial design to provide an optimal spray pattern of feedparticles across the catalyst particles. In an embodiment, the injectorsare attached to an annular oil ring or manifold surrounding the flow ofcatalyst particles in the riser reactor.

The injectors may be attached to the wall of the riser reactor or to theannular manifold such that the angle between the injector and the wallmay range from 0° to 90°. The riser reactor may be in a verticalposition at the point of feed injection, or the wall at the point ofinjection may deviate from vertical. If desired, more than one ring atdifferent levels may be employed. The riser reactor may also contain arefractory lining through which the injector passes.

It is preferred that the projection of the outlet of the feed injectorinto the flowing stream of catalyst particles in the riser be minimal sothat erosion of the outlet is minimized and that disturbance of thecatalyst stream is likewise minimized.

The following example is presented to illustrate the invention andshould not be considered limiting in any way.

EXAMPLE

In this example, an air/water feed was injected through the injectorshown in FIG. 4. The same feed was injected through a comparativeinjector which is identical to the injector shown in FIG. 4 except thatcomparative injector is in the form of a simple rectangle without thesaw-toothed pattern of protrusions shown in FIG. 4. The feed wasinjected through both injectors at comparable conditions (sametemperature, pressure and feed rate) so that the only variable was theconfiguration of the injector itself. The injector shown in FIG. 4 andthe comparative injector had a general aspect ratio of 3.2 and 3.6 and aratio of perimeter length-to cross-sectional area of 2.0 and 1.4respectively. The relative droplet size produced from the fan shapespray pattern produced by the respective injectors was measured as afunction of the distance from the center of the spray pattern. Theresults are shown in FIG. 5 in which the present invention is designatedas the STF Injector. As can be seen from FIG. 5, the relative dropletsize from the injector according to the invention is both smaller andmore uniform in size as compared to an injector without the saw-toothpattern.

1. A feed injector for atomizing a petroleum feed comprising: a conduitcontaining at least one inlet, at least one outlet and a passagewaywithin said conduit connecting the inlet with the outlet, saidpassageway containing an orifice wherein the orifice has a generalaspect ratio greater than 1.0 and a ratio of perimeterlength-to-cross-sectional area greater than 1.5 relative to aperimeter-to-cross-sectional area ratio of a circular orifice ofequivalent area, and the orifice includes at least one member protrudinginwardly from the perimeter of the orifice.
 2. The apparatus of claim 1wherein the orifice is elliptical or rectangular in shape.
 3. Theapparatus of claim 1 or 2 wherein the at least one inwardly protrudingmember comprises at least one pointed, square-edged or rounded member.4. The apparatus of claim 3 wherein the at least one inwardly protrudingmember is square-edged.
 5. The apparatus of claim 2 wherein the orificeis rectangular in shape.
 6. The apparatus of claim 5 wherein the orificecontains a plurality of square-edged protrusions protruding inwardlyfrom the rectangular shape.
 7. The apparatus of claim 1 wherein theorifice produces a fan-shaped spray pattern.
 8. The apparatus of claim 1wherein the general aspect ratio is greater than 1.5.
 9. The apparatusof claim 1 wherein the ratio of perimeter length-to-cross-sectional areais greater than 2.0.
 10. A process for injecting a petroleum feed into areaction zone of a fluid catalytic cracking reactor which comprises:injecting the feed into the reaction zone through a feed injector foratomizing the feed, said injector comprising a conduit containing atleast one inlet, at least one outlet and a passageway within saidconduit connecting the inlet with the outlet, said passageway containingan orifice wherein the orifice has a general aspect ratio greater than1.0 and a ratio of perimeter length-to-cross-sectional area greater than1.5 relative to a perimeter-to-cross-sectional area ratio of a circularartifice of equivalent area, and the orifice includes at least onemember protruding inwardly from the perimeter of the orifice.
 11. Theprocess of claim 10 wherein the orifice is elliptical or rectangular inshape.
 12. The process of claim 10 or 11 wherein the at least oneinwardly protruding member comprises at least one pointed, square-edgedor rounded member.
 13. The process of claim 12 wherein the at least oneinwardly protruding member is square-edged.
 14. The process of claim 10wherein the orifice produces a fan-shaped spray pattern.
 15. The processof claim 10 wherein the general aspect ratio is greater than 1.5. 16.The process of claim 10 wherein the ratio of perimeterlength-to-cross-sectional area is greater than 2.0.